Over the past few months, our Low Orbit Helium Assisted Navigator (LOHAN) spaceplane mission has been evolving with the help of you, our beloved reader experts.
Click here for a bigger version of the LOHAN graphic We've mulled various balloon configurations and launch platforms, checked out a possible rocket motor for the …

COMMENTS

Moment?

Just a bit concerned when the rockets fire they'll create a moment around the pivot/balloon which means she'll head off in any old direction, quite possibly straight downwards, or into the balloon. May need a bit of attention to make sure that's not the case!

Re: Moment?

Drooping Rod

I think an "I" section (that doesn't look right in this font, it's a capital i) rod, with teflon slider bits attached to LOHAN around the bottom flat part would be better than a circular rod.

You'd be able to support it all along the truss to avoid trouble with your rod drooping while inserted into LOHAN. It would also avoid any problems with her twisting on the shaft, and the associated friction problems.

Re: Why He?

You're overlooking one key aspect. Top boffinry demands that a pipe is smoked and chewed on throughout the experiment. The playmobil 'naut would be fine, but we need to reduce the risk on the ground for Lewis and his fellow boffins - rocket fuel is going to be hazardous enough! :-)

Re: Why He?

Slippery shaft

During this sort of process, according to Dr Spooner perhaps, you can expect a fair amount of falls and bucking - what measures will be in place to ensure LOHAN does not slip from her sturdy shaft prematurely, thus spoiling the climactic moment?

Halting yaw motion eases nerves but obviously you'd not want anything that impeded the thrust so a protective membrane that had to be pierced would not be appropriate.

Friction retards outward thrust so a ribbed section on the rod is probably not suitable either.

Having an integrated restraining yoke / combustible link attached medially may be the answer - allowing the fiery burst prior to the critical thrust stage to burn through when you really do want to let LOHAN loose.

Re: Hm... rubber.

Why a titanium rod?

The stuff is expensive and a bear to work with (it work-hardens). As LOHAN isn't exactly massive, a light alloy T extrusion should be fine. Mount it flat side down so LOHAN's Teflon sliders can clip over the edges.

Using a T should save structural weight too as it will be stiff enough to serve as the bottom member of an I-beam. Attach it to a carbon upper member with carbon diagonals to form a 2D launch track. You only need to fatten this to a 3D structure with a triangular or diamond cross section around the electronics. Adding a carbon cross-piece to steady the wings during the climb to launch height would be sensible, but you wouldn't need more than that because once LOHAN is moving longer wing steadies become irrelevant, particularly if the front half of the launch track is a 2D structure.

For that matter, the launch rail can almost certainly be a lot shorter then you've drawn it: any longer than LOHAN herself seems like overkill to me. The air up there is too thin for aerodynamic stability to have much, if any, effect during the launch and the further she slides on the rod the more friction will slow her down.

BTW, I think you need another test rig. It would be a good idea to test the eventual launch track, whatever its design turns out to be, by using smaller rockets at ground level. They should be wingless to approximate the lack of aerodynamic stability at 90,000 ft.

Re: Why a titanium rod?

If you have the engineering facilities it might also be worth putting a slight taper on both the rod and the sleeve(s) that LOHAN hangs on with. That way, as soon as it starts to move friction will rapidly fall away to virtually nothing.

Re: Why a titanium rod?

Re: Why a titanium rod?

I was wondering about the titanium rod myself. Conventional model rockets use an aluminum or steel rod. I get that LOHAN isn't exactly conventional, but surely she's not going to be putting much more stress on the launch rod than a ground based launch would.

There's little chance of a rod of any of these materials prematurely exploding while LOHAN is on them. You could make a stiff shaft out of any of them, and LOHAN would happily ride them into the heavens before getting off.

Why the blast deflector?

It’s not like you have anything to deflect the blast FROM — those are on ground-based pads to avoid setting grass fires. You’ll be about 15 miles too high to worry about that…

Also, what are the Teflon strips on the bottom edge of the truss for? They have no evident purpose.

Finally, I am in complete agreement about the use of a launch RAIL not a launch rod. It will be possible to get equivalent stiffness with far less mass if you are not depending on a single rigid mounting point. [ahem.]

Re: Why two elevons?

Two elevons because then they can control the aircraft properly. Rudder-only control is iffy at best. Sure it works, for a "you might end up ploughing into the floor at the slightest hint of a gust" definition of "works". Two properly positioned elevons give you pitch and roll, which is all you need. Yaw control would be nice, but hardly necessary when you're going to be landing in a field rather than on some narrow strip.

Moar Cameras.

Will we be having another attempt at trying to track it by telescope? Maybe some kind of auto-tracking tech following a radio beacon on the launch platform, if nobody can be bothered trying to move a scope around manually.

Also, I know you won't get a 3G signal all the way up there, but it might be worth having some kind of data feedback via mobile anyway, for when it gets low enough? Live webcam/telemetry feed from 10,000 feet and falling could be fun. Plus, it could help you locate the various parts a lot quicker than wandering around with a big antenna, signal meter and a map.

Oh, yeah.

About that launch rod. If it's hollow, try wrapping some resistive wire around something and stuffing it inside the rod. Approximately five minutes before launch, you have an alarm battery, or some kind of high-capacity LiPo start dumping current into the resistive wire. This heats it up, and removes any problem you might have about freezing the aircraft to the rail.

Re: Oh, yeah.

...that or a chemical reaction. Activated charcoal, rust and water are what's in heat packs. Fill the launch rod with it? Should be good for hours. Just needs to be hot enough to make the outside > 0C.

Re: Oh, yeah.

yeah, and then the rod expands and the sleeve thats made to slide freely on it doesn't expand as much so it seizes solid. Not really a good idea. Simply going for good tolerances and some low temp grease would work fine. (And using thermal coefficients the tolerances at altitude can be calculated rather easily)

I agree with the other commentards about just using a launch rail, not a rod. If you ARE hellbent on using a rod, go for a high grade steel, not titanium, which is complete overkill in this situation. On the short bit of rod used for LOHAN the gained strength is not really going to matter much, and the 40% weight saves is going to make little difference, if any. Titanium is a bitch to work/shape. It requires very sharp tools, high cutting speeds and lots of cooling. Get any of these wrong and you just ruin the material you are working on.

Then a simple contruction remark: Keep in mind that the same properties that make teflon nice and slippery also make mean nothing sticks to it, including glue. Any teflon parts will have to be screwed or locked in place by other means

Final remark, I would move the teflon sliding strips on the truss closer to LOHAN (or LOHAN closer to the strips). The shorter this distance is, the less momentum she can build up that would then need to be absorbed at impact. Yes, this could mean that the wings contact the strips more often, but that shouldn't really be a problem. If the swing is fast enough this could mean a lot of excess momentum that needs to be absorbed by the (probably) tiny flex of the wings skin. There is no other buffer.

Re: Oh, yeah.

Thermal expansion? The hottest the metal will get using heat packs is about 45C. So you do tests first, using worst possible case scenarios (ground level during a boiling Summer with a sleeve that's been resting in dry ice for instance), to see how loosely the sleeve needs to be fitted to the rod.

It's not like you're going to be needing micron accuracy just to make sure the Vulture 2 slides off the pole without sticking. Personally I'm hoping the rod, rail or whatever you want to use goes through the plane fuselage somehow, rather than through some non-aerodynamic externally-attached clamps. Use spring loaded flaps to close the entrance/exit holes afterwards.

And it'll still likely benefit from some kind of heating. A rod filled with chemical heat pack powder is just probably the easiest - and lightest - option. Remember that the original PARIS used low temperature grease, and that still stuck due to bits icing up.